1. Field of the Invention
The invention relates in general to elevator systems, and more specifically to new and improved supervisory system control and strategies for directing a plurality of elevator cars to answer calls for elevator service.
2. Decription of the Prior Art
Early attempts in the elevator industry to distribute calls for elevator service among a plurality of elevator cars set up service zones which extended from one car to the next busy car operating ahead of it. U.S. Pat. No. 2,064,045 is an example of this type of zoning. In U.S. Pat. No. 2,066,906 pushbuttons were provided at each landing for each car, with the service zone of a car illuminating the floor pushbuttons located at the floors of the service zone to indicate to prospective passengers which button to actuate in order to receive the most prompt service.
An early attempt at quota type control is disclosed in U.S. Pat. No. 2,020,981, which permitted an elevator car to stop only at those hall calls registered before it left the terminal. Later, quota controls were imposed on service zones. The quota mechanism could be set to prevent a car from appropriating more unanswered calls from its service zone at any one time than the quota, or it could be set to limit the number of stops a car made on a round trip by preventing the car from accepting any further calls once it had accepted its quota. U.S. Pat. No. 2,104,478 is an example of quota zoning.
Down peak zoning divides the building into zones during a down peak traffic condition to prevent inequitable service to the lower floors of the building. U.S. Pat. No. 2,376,113 reversed certain uptraveling cars at the highest call of the lower of two zones when the traffic level of the lower zone reached a predetermined magnitude. U.S. Pat. No. 2,447,935 reversed cars at the highest down call of a zone when the traffic level reached a predetermined level and there were no cars in the zone.
U.S. Pat. NO. 2,470,495 and 2,470,496 disclosed timed dispatching systems which automatically switched between a plurality of different traffic patterns based upon detected traffic conditions, including zoning during up peak and down peak conditions.
U.S. Pat. No. 3,256,958 discloses a zoned demand system, in which the elevator cars operate in response to demands, instead of a timed dispatching sequence.
U.S. Pat. No. 3,614,997 determines the traffic level in each car's service zone, and the traffic levels are summed and divided by the number of cars to obtain an average. This average traffic level in the zones is used to control spacing and work load of the cars by causing a car ahead of a car having a less than average work load to by-pass hall calls, and also to determine when a car is available for special direct service to a priority hall call.
U.S. Pat. No. 3,729,066 develops service zones between elevator cars and shifts the service zones to balance the service by generating imaginary positions of the cars, and considers the service zones from these imaginary positions.
The early supervisory system controls were relay implemented, while the later controls utilize solid state technology. The switch to solid state supervisory system control continued the philosophy of the large, complex relay implemented control, with the handling of the large amount of data associated with a plurality of elevator cars in a large building requiring either a complex hardwired logic system, or a powerful general purpose minicomputer. While these approaches are well suited for the larger banks of high speed elevators, it is too costly for the smaller banks of medium speed elevators.
The microprocessors, such as Intel's MCS-4 and MCS-8, Rockwell's PPS, Signetic's PIP, National's GPC/P and AMI's 7300, offer an attractive cost package as well as flexibility due to the LSI circuitry and programmability. The central processing unit (CPU) is usually a single chip, with the typical software package stored in companion reading-only-memories (ROMS). Data is stored in random access memories (RAMS).
While the microprocessor offers programming flexibility at a modest cost, it also imposes certain restrictions due to its relatively limited speed and memory capacity.
It would thus be desirable to provide a new and improved universal operating strategy for control of a group of elevator cars which will lend itself to use with a microprocessor, taking full advantage of the capabilities of the microprocessor, while working within its memory and speed limitations, to achieve fast, efficient elevator service for the floors of an associated building.